Techniques by which objects are located in three dimensional space span a broad range of scientific disciplines, the most typical involving optical or wave energy triangulation procedures and the like. The nature of the three dimensional space involved generally is primarily determinative of the approach taken by investigators in developing a mapping technique. Thus, visual access to the space, the conductive or magnetic character thereof and other aspects have a bearing upon the technical approaches taken.
Technologic developments in the field of medicine have involved the manipulation, in vivo or in vitro, of a wide variety of diagnostic and therapeutic probes and/or components through body tissues and cavities. This manipulation often requires an accurate monitoring of the location of such devices without incurring concomitant adverse influence upon the body tissue itself. In the latter regard, an avoidance of potentially damaging radiation interaction with the tissue may be important.
Medical procedures requiring a close, in vivo, monitoring of probe or component locations are those for example involving the use of heart catheters, coronary artery catheters or other internal body sensors. To avoid resort to open-heart surgery, a "pacemaker" type stimulator may be moved by catheters along a vena cava to the heart whereupon implantation is carried out by screw-attachment to muscle tissue. Power supply for the thus implanted stimulator then is more conveniently itself implanted for accessibility remote from the heart within the upper chest cavity. To the present, fluoroscopy, involving relatively higher levels of radiation is used to carry out probe position monitoring. Therapy involving the in vivo positioning of radioactive sources also requires precise position monitoring procedures to assure appropriate interaction of tissue being treated with emanating radiation. Where such implantation or probe positioning procedures are carried out, it is desirable that a precise monitoring of probe location be provided using a technique wherein accuracy is achieved without use of potentially harmful imaging or mapping systems.